Finite Element Based Transient Heat Transfer Analysis of Ti2AlNb Electron Beam Welds Using Hybrid Volumetric Heat Source

Abstract

Titanium based alloy Ti2AlNb is considered as a formidable structural material for advanced aero-engine applications due to its low density and high melting point temperature. Moreover, titanium based Ti2AlNb alloy is reactive towards atmospheric elements at an elevated temperature and hence conventional welding techniques do not fit to weld this type of materials. Furthermore, electron beam (EB) welding process is preferable to join Ti2AlNb alloy as it provides vacuum environment and possess high energy density with relatively minimum thermal input. EB welding produces deep and narrow penetration welds which leads to minimum weld induced stresses and distortion. In the recent past, several experimental analysis have been presented to comprehend the weld pool geometry during fusion welding procedures. Moreover, the phenomenological occurrence within and vicinity of the molten weld zone are primary focus of analysis. Therefore, a three-dimensional (3D) numerical model is paramount to interpret the physical occurrence of welding operation using a suitable volumetric heat source model. Nevertheless, in the current investigation, a transient heat transfer model based on finite element (FE) method is developed to simulate electron beam welds of titanium based Ti2AlNb alloy. In the course of modeling, a suitable thermal model is selected based on weldment profile and is quite accountable for determining accuracy of heat transfer analysis. The authors have considered a composite heat source model, comprising of two dimensional Gaussian distributed double ellipsoidal heat source at the top section and volumetric conical heat source through thickness of the cross section. Along with composite heat source model; material properties and latent heat of fusion as a function of temperature have been incorporated during modeling. The developed numerical heat transfer process model predicts the time-temperature history, cooling rates, weld bead dimensions and shapes. To verify the effectiveness of developed process model, the computed results are evaluated with experimentally estimated weld bead dimensions and profile. The numerical results indicated that the weld geometry characteristics and thermal history are in good accordance with the experimental data with less than 6% error. Moreover, the computed FE model results lays foundation for the estimation of welding induced distortion and residual stresses further.